UNIVERSITY    OF    CALIFORNIA    PUBLICATIONS 

IN 

AGRICULTURAL   SCIENCES 

Vol.  2,  No.  9,  pp.  249-296,  plates  45-52  December  31,  1924 


INHERITANCE  IN 
CREPIS  CAPILLAEIS  (L.)  WALLR.    III. 

NINETEEN  MORPHOLOGICAL  AND  THREE 
PHYSIOLOGICAL  CHARACTERS1 

BY 

J.  L.  COLLINS 


INTRODUCTION 

For  several  years  variations  in  Crepis  capillaris  have  been  studied 
genetically.  The  study  was  commenced2  in  the  hope  of  being  able 
to  determine  whether  the  extensions  of  the  Mendelian  theory  of 
heredity  which  were  based  on  breeding  data  from  Drosophila  melano- 
g aster  would  hold  for  higher  plants.  For  this  purpose  it  was  necessary 
to  know  the  mode  of  inheritance  of  a  number  of  characters.  This 
paper  is  concerned  with  the  description  and  mode  of  inheritance  of 
a  number  of  variations  found  in  Crepis  capillaris  (L.)  Wallr. 

It  is  evident  that  the  material  chosen  for  such  a  purpose  should 
show  variation  of  a  hereditary  nature  and  should  also  contain  a  low 
number  of  chromosomes.  Crepis  capillaris  seemed  to  fulfil  these 
requirements,  for  its  chromosome  number,  3  pairs,  is  the  lowest 
reported  for  the  higher  plants,  and  the  species  is  known  as  a  variable 
one. 

Linkage  has  been  demonstrated  in  a  number  of  plants  and  in  some 
of  the  higher  animals.  Unfortunately,  the  chromosome  number  in 
those  species  in  which  linkage  has  been  observed  is  relatively  high, 
and  in  no  case  is  the  number  of  groups  of  linked  genes  equal  to  the 
haploid  number  of  the  chromosomes. 


1  This  is  a  report  on  a  part  of  a  project  supported  by  appropriations  from  the 
Adams  Fund. 

2  Studies  commenced  by  Professor  E.  B.  Babcock  in  1915  and  carried  on  by 
the  writer  under  his  direction  since  1918;  published  as  nos.  6  and  7  of  vol.  2  in  the 
present  series. 


250  University  of  California  Publications  in  Agricultural  Sciences       [Vol.  2 

Material  and  Methods 

The  genus  Crepis,  containing  over  150  species,  is  a  member  of  the 
Cichorieae  or  chicory  tribe  of  the  Compositae,  the  best  known  related 
genera  being  Hieracium,  Lactuca,  Sonchus,  and  Taraxacum. 

Crepis  capillaris  (L.)  Wallr.  is  an  annual,  but  under  certain  cir- 
cumstances may  assume  the  biennial  habit.  The  plant  first  produces 
a  rosette  of  radical  leaves  which  have  been  found  to  vary  in  different 
plants  from  entire  to  bipinnately  compound.  The  stem  is  usually 
single  with  paniculate  branching  above  and  varies  from  a  few  inches 
to  four  feet  in  height,  largely  depending  upon  conditions  of  growth. 
The  cauline  leaves  are  sessile,  amplexicaul,  clasping,  the  lower  ones 
more  or  less  lobed  or  pinnatifid,  while  the  upper  ones  are  slender  and 
entire.  The  underside  of  the  midribs  of  the  rosette  leaves,  and  to 
some  extent  the  upper  side,  and  the  lower  cauline  leaves  are  more  or 
less  covered  with  bristly  hairs.  In  many,  but  not  all,  plants  the 
involucre  and  peduncle  are  glandular  pubescent  in  addition  to  the 
fine  gray  tomentum  which  is  always  present.  The  brown  terete 
achenes  vary  in  length  from  2  to  3  mm.,  are  attenuate  at  both  apex 
and  base,  and  usually  10-ribbed.  The  yellow  flower  heads  vary  from 
17  to  25  mm.  in  diameter. 

During  the  course  of  the  investigations,  achenes  of  C.  capUlaris 
have  been  obtained  from  many  localities  of  the  temperate  and  sub- 
tropical zones  of  both  the  old  and  the  new  world.  The  species  is 
apparently  a  native  of  Europe,  but  is  now  disseminated  throughout 
the  world. 

The  methods  used  in  growing  experimental  cultures  of  Crepis 
have  been  previously  published  (Collins,  1922). 

In  presenting  data  from  hybrid  populations,  the  degree  of  corre- 
spondence of  observed  with  calculated  distribution  has  been  deter- 
mined by  use  of  tables  of  probable  errors  of  Mendelian  ratios  prepared 
by  the  Department  of  Plant  Breeding  of  Cornell  University.  In  the 
case  of  some  dihybrid  populations  the  method  suggested  by  Harris 

(0  C)2 

(1912)  has  been  used.     This  formula  is  X2  =  2- ,  in  which  o 

c 

is  the  observed  frequency  of  any  class,  c,  the  calculated  frequency  for 

(0 c)2 

that  class,  and  2  indicates  that  all  the  values  of  the  type ■  are 

c 

added  together.  From  Elderton's3  tables  for  calculating  the  goodness 
of  fit,  the  probability  for  the  chance  occurrence  of  the  deviations  in 
the  observed  classes  has  been  obtained  from  the  calculated  value  of  X2. 


3  Given  in  Pearson,  K.,  Tables  for  Statisticians  and  Biometricians,  Cambridge 
Univ.  Press,  1914. 


1924] 


Collins:  Inheritance  in  Crepis  capillaris   (L.)    Wallr. 


251 


VARIATIONS  IN  CREPIS  CAPILLARIS 

Observations  upon  cultures  grown  from  the  achenes  obtained  from 
localities  in  many  different  regions  have  resulted  in  the  discovery 
of  a  number  of  variations.  Those  which  have  been  studied  sufficiently 
to  show  their  method  of  inheritance  are  described  below.  In  assign- 
ing symbols  to  serve  as  genetic  representatives  of  particular  char- 
acters, the  system  in  general  use  has  been  followed,  namely,  the  use 
of  the  initial  letter  (or  letters)  of  the  name  given  to  the  character, 
small  letters  indicating  a  recessive,  and  capital  letters  a  dominant 
condition. 

BALD  (b) 

On  August  17,  1918,  a  single  plant  (19.18P23)  in  a  culture  of  47 
plants  grown  from  achenes  sent  from  Copenhagen  was  found  to  be 
devoid  of  glandular  pubescence  on  the  involucre  and  peduncle.  This 
variation  has  been  named  '  bald. '  The  second  instance  of  this  variation 
was  in  the  same  race  but  appeared  only  after  two  generations  of 
inbreeding.  Bald  plants  later  appeared  in  cultures  from  other  locali- 
ties as  follows:  Sweden,  England,  France,  Chile,  and  the  Azores.  It 
was  of  importance  to  know  whether  the  same  or  different  genes  were 
responsible  for  the  appearance  of  'bald'  in  cultures  from  such  widely 
separated  sources.  This  could  be  determined  by  crossing  the  different 
races.  If  a  single  gene  were  involved,  then  bald  Fx  plants  should 
result,  while  if,  on  the  other  hand,  glandular  plants  resulted  in  the 
Fx,  this  variation  appearing  in  the  different  stocks  would  be  the 
similar  expression  of  different  genes.  As  is  shown  in  table  1,  the 
same  gene  is  present  in  each  case. 

TABLE  1 

The  Fi  Results  of  Crossing  Different  Geographical  Races  of  Bald 


Character  of  Fi 

Culture  No. 

Bald 

Glandular 

Total 

F2  Copenhagen  X  Sweden  (20.130)  X  Chile  (21.23).. 
Sweden  (19.235)  X  Cambridge  (19.66) 

9 
4 

56 
1 

7 

0 
0 

0 
0 
5 

9 
4 

Copenhagen    (18.75)  X  Sweden    (19.235)    (19.H1, 
20.57-8,  21.101) 

56 

Chile  (20.36)  X  Azores  (20.40),  (21.25). 

1 

Sweden  (19.H3)  X  Azores  (20.40),  (21.117) 

12 

252 


University  of  California  Publications  in  Agricultural  Sciences       [Vol.  2 


In  the  last  item  in  table  1  both  bald  and  glandular  plants  are 
recorded.  This  is  as  it  should  be,  for  the  19. H3  plant  was  an  Fx 
glandular  plant  produced  by  crossing  the  Swedish  bald  race  (19.235) 
with  a  Eureka  glandular  race    (19.224).     If  the  bald  gene  in  the 


TABLE  2 
F,  Eesults  from  Crosses  of  BB  X  bb 


Character  of  Fi  plants 

Pedigree  No. 

Glandular  (B) 

Bald  (b) 

19.H3 

20.59 

21.21 

21.28 

2 
10 

7 
7 

0 
1 
2 
0 

Total 
Expected  1 : 0 

26 
29 

3 
0 

TABLE  3 
Back  Crosses  of  the  Fn  Bb  to  bb 


Pedigree  No. 

Progeny  segregation 

B 

b 

21.17 

21.18 

21.19 

21.24 

21.117 

21.126 

7 
5 
6 
4 
12 
4 

3 
6 
7 
2 
13 
2 

Total 
Calculated  1 :1 

39 
38.5 

38 
38.5 

Deviation 

0.5  ±  3.84 

cultures  from  Sweden  and  from  the  Azores  were  identical,  we  should 
expect  to  obtain  from  such  a  back  cross  50  per  cent  glandular  and 
50  per  cent  bald  plants.  The  5  to  7  segregation  obtained  is  a  close 
approximation  to  the  expected  1  to  1  ratio.  While  the  Copenhagen 
race  has  not  been  crossed  with  the  Cambridge  race,  nor  the  Chilean 


1924 


Collins:  Inheritance  in  Crepis  capillaris   (L.)    Wallr. 


253 


race  with  any  except  that  from  the  Azores,  we  have  evidence  of  their 
identity,  since  they  have  each  been  crossed  with  the  Swedish  race, 
which  in  turn  was  proved  to  be  identical  with  the  others.  The  bald 
plants  from  France  have  not  been  tested.  Bald  is  inherited  as  a 
simple  monohybrid  recessive,  as  is  shown  by  the  results  obtained  from 
crossing  with  glandular  plants.  Table  2  presents  Fx  data  from  crosses 
of  bald  X  glandular.  The  one  bald  plant  in  culture  20.59  probably 
resulted  from  the  failure  to  remove  a  single  pollen  grain  during 
emasculation  and  represents  an  error  in  technique.     The  two  bald 

TABLE  4 
F2  Results  prom  the  Cross  BB  X  bb 


Progeny  segregation 

Pedigree  No. 

B 

b 

20.59 

20.60 

20.141 

20.142 

20.118 

10 

2 

56 

16 

74 

1 
3 

17 
7 

23 

Total 
Calculated  3:1 

158 
156.75 

51 
52.25 

Deviation 

1.25  db  4.22 

plants  in  culture  21.21  may  be  ascribed  to  this  same  cause  or  to  errors 
at  time  of  transplanting,  since  culture  21.23,  containing  only  bald 
plants,  grew  adjacent  to  21.21  in  the  flat  before  transplanting  to  the 
field. 

Table  3  shows  that  39  glandular  to  38  bald  plants  were  obtained 
when  the  Fx  (bald  X  glandular)  were  backcrossed  to  the  recessive 
parent  strain.    The  expected  1  to  1  ratio  was  therefore  realized. 

The  results  from  F2  cultures  confirm  the  conclusion  regarding  a 
single  recessive  factor  conditioning  the  appearance  of  bald.  While 
in  almost  all  cases  involving  bald  the  glandular  hairs  are  completely 
absent,  in  culture  20.141  some  plants  appeared  to  be  somewhat  inter- 
mediate, inasmuch  as  they  developed  a  few  small  scattered  gland  hairs 
on  the  involucre.  They  were  easily  distinguishable  from  glandular 
plants.     In  table  4  these  intermediates  have  been  classified  as  bald, 


254  University  of  California  Publications  in  Agricultural  Sciences       [Vol.  2 

but  in  the  original  records  they  were  designated  as  intermediates. 
If  the  culture  20.141,  containing  the  intermediate-bald  plants,  is 
removed  from  the  table,  the  remaining  cultures  give  an  exact  ratio 
of  3  glandular  to  1  bald;  when  the  intermediates  are  classified  as 
bald,  the  deviation  from  a  3  to  1  ratio  is  less  than  the  probable  error. 
The  progeny  of  two  bald  and  two  glandular  F2  plants  were  grown. 
Both  of  the  former  gave,  as  expected,  only  bald  offspring,  while  the 
two  glandular  F2  plants  produced  both  types  in  F3. 

The  nature  of  the  intermediate  plants  has  not  been  definitely 
determined.  The  selfed  progeny  from  one  plant  (18.dlP76)  gave  a 
culture  (20.55)  of  18  bald,  3  intermediate,  and  3  glandular  plants. 
That  they  were  not  due  to  the  incomplete  dominance  of  the  hybrid 
produced  by  crossing  bald  with  glandular  is  certain,  for  in  the  Fx 
cultures  (table  2)  all  plants  were  fully  glandular.  Another  inter- 
mediate bald  plant  (22.153P18)  produced  5  glandular  and  5  bald 
plants  from  selfed  seed  but  none  that  could  be  classified  as  inter- 
mediate. 

SMOOTH    MIDEIBS   (s) 

The  midribs  of  the  rosette  leaves  usually  have  a  hairy  pubescence. 
From  sporadically  appearing  plants,  races  have  been  obtained  which 
do  not  show  these  rib  hairs;  such  plants  have  been  designated  as 
*  smooth'  (s).  The  Fx  resulting  from  a  cross  between  these  two  types 
of  plants  were  all  rib-haired,  and  in  the  F2  there  appeared  556  rib- 
haired  to  40  smooth  plants.  This  is  approximately  a  15  to  1  ratio 
and  suggests  the  operation  of  two  independent  genes,  each  producing 
the  same  somatic  effect. 

Duplicate  genes  are  by  no  means  unknown,  having  been  reported 
a  number  of  times  in  the  literature  of  genetics.  If  two  independent 
genes  were  operating  in  the  cultures  21.140  and  21.141,  the  Fx  of 
this  same  cross  when  backcrossed  to  smooth  should  give  a  3S  to  Is 
ratio  and  some  F3  populations  should  give  a  3  to  1  segregation. 
Evidence  from  cultures  of  these  two  types  has  been  obtained;  the 
data  from  them  together  with  data  from  other  crosses  involving  this 
character  are  given  in  table  5.  The  F3  culture  21.189  was  grown  from 
one  plant  of  an  F2  culture  containing  58  rib-haired  and  no  smooth 
plants.  Such  a  deviation  is,  however,  only  three  times  the  probable 
error  and  may  well  be  due  to  errors  of  random  sampling.  The  culture 
Fi  19. HI  was  originally  made  to  determine  the  relation  of  the  gene 
for  bald  of  the  English  race  of  Crepis  to  that  in  the  Danish  race  and 


1924 


Collins:  Inheritance  in  Crcpis  capillaris   (L.)    Wallr. 


255 


was  the  hybrid  between  these  two  races.  The  parent  plant  from  the 
English  race  was  smooth,  while  the  parent  from  the  Danish  race  had 
rib  hairs. 

TABLE  5 
Showing  F,  and  F3  Results  from  the  Cross  SSS'S',  SSs's',  and  SsS's' 

WITH    SSS'S' 


Progeny  segregal 

ion 

Pedigree  No. 

S 

s 

F2  21.140 

237 

17 

F2  21.141 

319 

23 

F3  22.189 

Total 

189 

9 

743 

49 

Cal( 

mlated  15:1 
Deviation 

742.5 

49.5 

0.5  ±  4.59 

F2  22.55 

25 

12 

F2  22.56 

5 

2 

F2  22.60 

22 

6 

F2  22.61 

4 

2 

F2  22.62 

9 

1 

F2  22.63 

34 

8 

F2  22.41 

Total 

66 

24 

165 

55 

Ca 

Iculated  3:1 
Deviation 

165 

55 

0.0  ±  4.52 

Back 

cross  19. HI 

55 

17 

Ca 

Iculated  3:1 
Deviation 

54 

18 

1.0  db  3.83 

The  3  to  1  ratio  obtained  in  19. HI  indicates  that  the  rib-haired  2 
used  was  heterozygous  for  the  duplicate  genes  for  rib  hairs.  This 
cross,  as  regards  these  characters,  was  a  back  cross  of  a  heterozygote 
to  the  recessive  parent,  and  constitutes  additional  evidence  to  sub- 
stantiate the  duplicate  gene  interpretation  given  above  for  the  inherit- 
ance of  rib  hairs  in  these  cultures. 


256  University  of  California  Publications  in  Agricultural  Sciences       [Vol.  2 


LEAF  VARIATIONS 

From  the  very  first  acquaintance  with  C.  capillaris,  the  different 
forms  in  the  rosette  leaves  constituted  the  most  striking  and  out- 
standing variations.  They  have  proved  equally  as  difficult  to  study 
genetically,  due,  first,  to  the  difficulty  in  evaluating  non-genetic 
variability  resulting  from  age  of  plant  and  from  environmental  causes, 
and,  second,  to  the  complex  heterozygotic  nature  of  the  material  in 
the  wild  condition.  Sears  (1921)  found  in  T araxacum  that  the  degree 
of  leaf  dissection  is  correlated  with  the  age  of  a  given  rosette.  The 
leaves  of  a  very  young  rosette  are  almost  entire,  becoming  progres- 
sively more  dissected  as  the  rosette  becomes  older.  Stork  (1920), 
also  working  with  Taraxacum,  found  that  in  very  young  plants 
the  rosette  leaves  ranged  in  form  from  entire  to  deeply  pinnatifid- 
runcinate,  but  became  more,  instead  of  less  uniform,  as  they  grew 
older.  Neither  condition  can  therefore  be  taken  as  typical  for  that 
species.  In  Crepis,  a  closely  related  genus,  there  is  a  more  regular 
sequence  of  development  of  leaf  shape  for  a  particular  rosette.  The 
juvenile  leaves  are  usually  entire  or  nearly  so,  and  assume  their 
typical  forms  gradually  as  the  plant  reaches  the  mature  rosette  stage 
just  preceding  the  appearance  of  the  flowering  stalk.  At  this  time 
there  exist  individual  differences  which  range  in  form  from  entire 
to  deeply  pinnatifid  or  compound  pinnatifid.  That  these  differences 
are  genetic  is  shown,  first,  by  the  fact  that  inbreeding  has  resulted 
in  the  isolation  of  races  of  the  different  types  which  breed  true  when 
grown  side  by  side  under  similar  conditions,  thus  to  a  large  degree 
eliminating  the  effect  of  the  non-genetic  factors,  and,  second,  that 
the  forms  when  crossed  give  a  fairly  uniform  Fx  and  segregate  into 
the  parental  and  Fx  forms  in  the  second  generation. 

By  means  of  inbreeding  and  selection,  a  number  of  distinctive, 
uniform  races  have  been  obtained  in  almost  homozygous  condition. 
A  brief  description  of  each  is  given  below. 

VIEIDIS 
Plate  45,  figure   1 

This  form  was  isolated  in  1919  from  the  Eureka  (California) 
stock.  The  rosettes  are  small,  4  to  10  inches  in  diameter.  The  leaves 
are  deeply  lobed  or  pinnately  parted,  and  are  lacking  in  anthocyanin. 


1924]  Collins:  Inheritance  in  Crepis  capillaris   (L.)    Wallr.  257 

The  blade  of  the  leaf  is  of  a  darker  color  than  the  midrib.  The  color 
of  the  blade  is  Ridgway's  varleys  green,  31'  m.  The  midrib  is  covered 
on  both  upper  and  lower  surfaces  with  hairy  pubescence.  The  lobes 
are  usually  widest  at  the  base,  often  having  a  minor  lobe  attached  to 
the  proximal  edge  of  the  base  of  the  major  lobe.  Attached  to  the 
midrib  between  the  lobes  is  a  narrow  wing.  The  lobes  are  usually 
close  together,  with  the  terminal  lobe  slender  and  pointed. 

H6  RACE 
Plate  45,  figure  2 

The  H6  race  was  isolated  in  1919  from  a  Berkeley  Crepis  stock. 
The  size  of  the  rosettes  is  more  variable  than  in  viridis,  the  rosettes 
ranging  from  8  to  12  inches  in  diameter.  The  leaves  are  pinnately 
and  bipinnately  lobed ;  the  lobes  are  constricted  at  the  base  and 
rounded  at  the  tip,  and  inclined  to  twist,  so  that  the  plane  of  the  lobe  is 
not  in  the  same  plane  with  the  midrib.  Anthocyanin  is  conspicuously 
present.  There  are  no  hairs  on  the  midrib.  The  lobes,  usually  six 
in  number,  are  widely  spaced.  The  terminal  lobe  is  large  and  blunt- 
tipped.  The  narrow  wing  on  the  midrib  is  crimped,  presenting  a 
ruffled  effect.  The  wing  and  edges  of  the  lobes  contain  a  blackish 
purple  coloring  which  appears  very  early  in  the  development  of  the 
plant.  The  leaf  color,  according  to  Ridgway's  Standard,  is  cedar 
green,  31m.  The  characters  which  make  up  this  type  are  dominant, 
excepting  smooth  ribs,  when  crossed  with  viridis. 

PALLID 
Plate  45,  figure  1 

This  race  was  obtained  in  1919  by  inbreeding  in  the  same  Eureka 
stock  that  produced  the  viridis  race.  The  rosettes  are  from  6  to  10 
inches  in  diameter.  This  race  produces  more  leaves  in  the  rosette 
than  do  the  preceding  races,  giving  the  rosette  a  thick  mat-like  appear- 
ance. Pallid  lacks  anthocyanin  and  is  a  much  paler  green  (Ridgway's 
forest  green,  29'm.)  than  the  two  races  described  above.  The  lobes 
are  broadest  at  the  base,  are  set  closely  together,  and  have  pronounced, 
pointed  teeth.  This  race  does  not  grow  so  rapidly  as  the  darker  green 
races.     Rib  hairs  are  present  on  the  midrib. 


258  University  of  California  Publications  in  Agricultural  Sciences       [Vol.  2 

SIMPLEX  Z9 
Plate  46,  figure  1 

Simplex  Z9  was  isolated  in  1920  from  a  stock  originating  from 
seed  collected  at  Quy  Fen,  England.  The  original  culture  consisted 
of  plants  ranging  from  entire  to  pinnatifid.  The  simplex  Z9  race  was 
obtained  by  inbreeding  plants  with  entire  leaves.  Although  inbreed- 
ing has  reduced  the  amount  of  variation,  there  still  appears  in  this 
supposedly  homozygous  race  a  small  percentage  of  semi-pinnatifid- 
leaved  plants  (pi.  46,  fig.  1).    Anthocyanin  and  rib  hairs  are  present. 

SCALAEIS  e29 
Plate  46,  figure  2 

This  race  was  isolated  in  1919  from  the  Eureka  stock  of  Crepis 
which  produced  the  viridis  and  the  pallid  races.  It  is  characterized 
chiefly  by  long,  simple,  pinnately-divided  leaves  with  pointed  lobes. 
The  terminal  lobe  is  slender  and  elongated,  often  curved  to  one  side 
near  the  tip.  Both  anthocyanin  and  rib  hairs  are  present.  The 
average  number  of  lobes  per  leaf  is  10.  It  is  clominent  when  crossed 
with  simplex  Z9  or  with  viridis.  Typical  leaves  of  the  scalaris  e29 
and  the  simplex  Z9  races  are  shown  in  plate  52,  together  with  the 
Fx  and  F2  types  obtained  when  these  two  races  are  crossed.  In  the 
F1  a  few  extreme  variants  occur  which  approach  the  simplex  form, 
but  the  majority  are  more  nearly  like  the  scalaris  and  constitute  a 
fairly  uniform  intermediate  type.  In  the  F2,  three  types  are  dis- 
tinguishable (see  pi.  51,  fig.  2),  the  two  grandparental  forms  and  an 
intermediate  scalaris  form  similar  to  the  F1.  When  the  intermediate- 
scalaris  and  the  scalaris  are  grouped  together  a  3  to  1  ratio  is  obtained 
(see  table  6)..  The  intermediate  forms  differ  from  the  scalaris  in 
having  the  lobes  less  deeply  incised,  some  more  so  than  others,  but 
still  classifiable  as  intermediate.  (See  third  and  fourth  leaves  in 
P2,  pi.  52.) 

From  the  results  of  breeding  it  appears  that  there  is  present  one 
main  gene  for  lobing  and  that  dominant  modifying  genes  are  involved 
which  act  cumulatively,  thus  producing  intermediates  of  different 
grades  of  pinnate  lobing.  As  a  corollary  to  this  hypothesis  races 
breeding  true  for  different  grades  of  intermediate  pinnatifid  lobing 
should  be  possible.  There  is  evidence  that  such  races  occur.  Several 
intermediate  forms  have  been  tested  and  found  to  be  fairly  constant. 


1924 j  Collins:  Inheritance  in  Crcpis  capillaris   (L.)    Wallr.  259 

A  race  obtained  from  Seattle,  Washington  (named  "Seattle") 
appears  to  be  such  a  homozygous  intermediate  form. 

Races  of  Crcpis  capillaris  also  differ  in  number  of  lobes  per  leaf 
and  in  length  of  leaf  (Rau,  1923).  The  scalaris  race  shown  in  plate 
52  has  a  large  number  of  lobes.  The  two  races  differ,  however,  in 
length  of  leaf.  The  leaves  of  the  scalaris  parent  shown  in  plate  52 
are  shorter,  and  of  the  simplex  parent  larger,  than  the  mean  size 
typical  for  each  race.  The  Fx  is  usually  larger  than  either  parent. 
The  F2  in  the  same  figure  shows  the  segregation  for  size  which  appears 
to  be  due  to  multiple  genes. 

The  inheritance  of  pinnatifid  and  entire  leaf  forms  in  capillaris 
conforms  in  general  to  the  type  of  inheritance  of  corresponding  forms 
in  a  number  of  other  plants.  Rasmusen  (1916)  found  in  species 
crosses  in  grapes  that  differences  in  leaf  form  behaved  in  a  very 
similar  way.  The  F1  appeared  to  be  intermediate  between  the  shapes 
of  the  parent  leaves.  In  the  F2,  a  series  was  produced  which  included 
the  grandparental  forms,  the  Fx  type  and  different  grades  of  inter- 
mediates. If  the  deeply  toothed  and  intermediate  toothed  classes  were 
grouped  together,  a  ratio  of  3  toothed  to  1  non-toothed  resulted. 

Shull  (1918)  found  four  different  leaf  forms  of  the  shepherd's 
purse  to  be  caused  by  two  pairs  of  factors.  As  in  Crcpis,  the  deeply 
pinnatifid  forms  were  dominant.  The  plants  were  also  subject  to 
considerable  fluctuating  variation.  Two  races  of  Urtica,  one  having 
deeply  serrated  leaves,  the  other,  leaves  with  entire  edges,  gave 
serrated  leaves  in  Fx  and  a  ratio  of  3  serrated  to  1  entire  leaf  in 
the  F2  generation  (Correns,  1912).  In  cotton,  however,  the  deeply 
palmately  parted  leaf  form  is  not  dominant  when  crossed  with  the 
five-pointed  upland  type,  but  produces  an  intermediate  type  in  Ft 
with  a  ratio  of  1:2:1  in  the  F2  generation  (Shoemaker,  1909). 
Kristofferson  (1923)  found  that  the  difference  in  lobing  of  the  leaves 
of  two  species  of  Malva  was  brought  about  through  a  single  genetic 
factor,  and  resulted  in  a  somewhat  intermediate  condition  in  Fx  and 
a  3  lobed  to  1  non-lobed  condition  in  the  F2,  although  considerable 
variation  in  the  degree  of  lobing  in  the  pinnatifid  class  was  recognized. 
Tedin  (1923),  on  the  other  hand,  found  that  pinnatifid  and  entire 
leaved  plants  differed  genetically  by  two  factors. 


260 


University  of  California  Publications  in  Agricultural  Sciences       [Vol.  2 


TABLE  6 
The  Eesults  from  the  Cross  of  Leaf  Forms.    Sc  X  sc 


Progeny  segregation 

Pedigree  No. 

Sc 

sc 

21.140 

22.7 

22.10 

22.14 

22.17 

22.19 

22.22 

22.24 

22.25   . 

22.26 

177 
99 
50 
14 
48 
92 

167 
51 
37 
29 

75 
24 
17 

6 
15 
19 
52 
14 
13 

2 

Total 
Calculated  3:1 

764 
750.75 

237 
250.25 

Deviation 

13.25  ±  9.24 

SCALARIS  e28  (Sc) 
Plate  47,  figure  1 

This  pinnatifid  leaf  form  was  isolated  in  1919 ;  it  originated  from 
a  single  plant  which  was  a  sib  to  the  one  producing  the  scalar  is  e29 
race.  These  two  forms  have  much  in  common,  but  are  different  in 
size,  e28  being  smaller  and  not  so  vigorous  as  e29,  and  having  shorter 
and  blunter  lobes. 

Two  races  of  the  pinnatifid  leaf  forms  isolated  from  the  Berkeley 
(H6)  race  of  plants  and  from  the  Eureka  population  (e28),  respec- 
tively, differ  in  a  number  of  minor  characters,  as  shown  in  the  follow- 
ing comparative  list : 


H6  (Berkeley) 
dark  green 
dark  green  to  blackish 
pronounced 
pronounced 
none 

pronounced 
blunt  and  rounded 
rounded 
wide   (very) 
pronounced 
large 


Characters 
color  of  leaf 
color  of  midrib 
anthocyanin 
crimping  of  rib-wing 
rib  hairs 

black  edge  on  leaf 
terminal  lobe 
lateral  lobe 
lobe  spacing 
Constricted  base  of  lobes 
secondary  lobes 


e28  (Eureka) 
dark  green 
light  green 
none  or  trace 
none 
present 
trace  only 
narrow — pointed 
slender — more  pointed 
wide    (medium) 
none  or  trace 
none 


1924] 


Collins:  Inheritance  in  Crepis  capillaris   (L.)    Wallr. 


261 


Plants  of  these  two  races  when  crossed  showed  almost  the  entire  group 
of  H6  characters  (rib  hairs  excepted)  in  the  ¥1,  while  in  P2  (21.141) 
there  appeared  the  parental  types  and  in  addition  some  composite 
types  that  showed  some  characters  from  each  parent.  When  each 
character  pair  was  considered  separately,  however,  a  peculiar  sit- 
uation was  presented.  Six  of  the  character  pairs  gave  9  to  7  ratios, 
and  a  seventh  pair,  rib  hairs  vs.  smooth  ribs,  gave  a  15  to  1  ratio. 
The  data  for  these  characters  are  included  in  table  7.  It  is  quite 
probable  that  these  six  character  pairs  as  given  are  the  result  of  not 
more  than  three  sets  of  genes,  since  the  two  characters,  black  edging 
of  the  leaves  and  anthocyanin  of  the  midribs,  are  both  concerned  with 
the  distribution  of  anthocyanin  pigment  in  the  plant.  The  shape  of 
the  terminal  and  of  the  lateral  lobes  is  probably  conditioned  by  the 
same  pairs  of  genes,  while  the  crimping  of  the  wing  of  the  midrib 
and  the  constriction  of  the  base  of  the  lobes  also  probably  result  from 
the  action  of  the  same  gene.  The  Berkeley  plants  were  evidently 
homozygous  for  the  dominant  complementary  genes  of  all  three 
character  couples.  This  genotype  may  be  expressed  as  AA'BB'CC, 
the  simultaneous  presence  of  both  the  primed  and  unprimed  dominant 
genes  being  necessary  to  cause  the  development  of  the  respective 
characters.  The  Eureka  race  would  then  have  the  genotype  aa'bb'cc' 
with  respect  to  these  characters. 

TABLE  7 

Segregation  of  Six  Pairs  of  Characters  in  the  F2  from  the  Cross 
H6  X  Scalaris  e28.     (Culture  21.141) 


Segregation 

Calculated 
9  :7 

Deviation 

162  black  edge  :  103  green  edge 

149.06  :  115.93 
154.71  :  120.33 

143.1     :  111.3 
143.1     :  111.3 

143.1     :  111.3 
149.58  :  116.34 

12.94  ±  5.45 

166  anthocyanin  :  109  none 

11.29  ±  5.55 

142  angular  lobes  :  112  round 

1.1     ±  5.33 

150  narrow  lobes  :  104  broad  lobes 

6.9    ±  5.33 

135  constricted  lobes  :  118  non-constricted 

165  crimped  wing  :  101  flat  wing 

8.1     ±  5.32 
15.42  ±  5.49 

BEVOLUTE  (r) 

Plate  47,  figure  2 
This  race  appeared  in  1919  among  offspring  of  a  plant  of  the 
Eureka  stock,  which  had  been  self -pollinated.     The  plants  are  char- 
acterized by  a  definite  downward  curling  of  the  edge  of  the  leaf 


262 


University  of  California  Publications  in  Agricultural  Sciences       [Vol.  2 


toward  the  midrib.  It  occurs  in  both  entire  and  pinnatifid  types, 
though  it  is  more  conspicuous  in  the  former.  In  appearance  much 
like  the  fwmfolia  mutant  of  Oenothera  Lamarckiana  described  by 
Shull  (1921),  in  which  both  rosette  and  cauline  leaves  have  edges 
curled  under.  The  knowledge  of  the  genetic  basis  for  this  character 
has  been  obtained  incidentally  in  experiments  designed  to  show  in- 
heritance of  other  characters.  The  data  thus  obtained  indicate  that 
revoluteness  is  conditioned  by  complementary  recessive  genes. 


TABLE  8 
Showing  the  Segregation  of  Eevolute  Leaves  in  Two  Cultures 


Progeny  segregation 

Pedigree  No. 

R 

r 

19.e5 
Calculated  3:1 

62 
59.25 

17 
19.75 

Deviation 

2.75  ±  2.60 

21.140 
Calculated  15:1 

233 
237.19 

20 
15.81 

Deviation 

4.19  ±2.60 

It  is  significant  that  revolute  appeared  only  in  these  two  cultures, 
which  were  derived  from  a  common  source,  because  it  indicates  that 
the  genes  were  present  in  the  wild  plants  from  which  the  starting  point 
of  these  cultures  was  obtained.  The  15  to  1  ratio  made  its  appearance 
in  the  sixth  generation  from  the  wild  plants  (some  out-crossing  occurs 
in  this  pedigree),  while  the  3  to  1  ratio  appeared  in  the  second  gen- 
eration. 

BICEPHALIC  (bi) 
Plate  48,  figure  1 
This  character  designates  a  type  of  fasciation  in  which  the  buds 
are  more  or  less  joined  together  in  twos.  The  peduncle  is  also  fre- 
quently flattened.  This  variation  was  first  found  in  1920  on  a  single 
plant  (20.30)  which  was  grown  from  achenes  obtained  from  Chile. 
This  original  plant  was  crossed  with  20.130P19,  which  produced  an 
Fx  culture  of  9  normal  plants.  The  F2,  consisting  of  81  plants,  segre- 
gated into  60  normal  to  21  bicephalic,  clearly  a  monofactorial  ratio. 


1924J 


Collins:  Inheritance  in  Crepis  capillaris   (L.)    Wallr. 


263 


In  no  case  were  all  the  buds  of  a  plant  of  the  bicephalic  kind.  Some 
plants  indeed  produced  only  a  few  double  buds.  F2  bicephalic  plants 
of  both  types  were  selfed  and  F3  cultures  produced.     The  data  from 


F3  cultures  are  shown  in  table  9. 


TABLE  9 

Type  of  Plants  Produced  by  Selfing  F2  Bicephalic  Plants 


F2  Plant  No. 

Progeny  F3 

23.283 

Bicephalic 

Normal 

*P68   + 

6 

1 

P70  + 

2 

6 

P96   + 

8 

0 

P«     +  + 

6 

0 

P10+  + 

6 

0 

P23   +  + 

5 

1 

P24+  + 

2 

0 

P30+  + 

0 

1 

P44+  + 

20 

0 

P46+  + 

8 

0 

P48+  + 

5 

2 

P57+  + 

2 

0 

P8l+  + 

5 

(2?) 

*  The  single  +  indicates  an  F2  plant  on  which  but  few  bicephalic  buds  appeared. 
The  ++  indicates  plants  having  many  such  buds. 

It  appears  that  F2  bicephalic  plants  breed  true  in  F3.  Plant  70 
which  had  only  a  few  double  buds,  was  apparently  a  heterozygote,  for 
it  gave  a  3  to  1  ratio  in  F3.  The  other  F3  plants  listed  as  normal 
may  have  been  genetically  bicephalic,  since  they  showed  some  evi- 
dences of  f asciation  in  the  stems  and  malformation  of  buds ;  but  no 
doubling  or  cohesion  of  the  buds  was  found. 


ANTHOCYANIN 

This  pigment  is  distributed  to  many  parts  of  the  plant,  but  is 
most  noticeable  in  the  midribs  of  the  leaves  and  on  the  lower  portions 
of  the  stems.  Culture  19.e8  segregated  into  94  plants  with  antho- 
cyanin  to  39  with  none  or  developed  only  to  a  slight  degree.  The  ratio 
in  this  case  is  2.82  to  1.17,  in  which  the  deviation  is  less  than  twice 
the  probable  error.  This  segregation  can  be  considered  only  as  sug- 
gestive because  of  the  difficulty  of  accurately  classifying  this  character 


264  University  of  California  Publications  in  Agricultural  Sciences       [Vol.  2 

in  Crepis.  The  appearance  of  purple  anthocyanin  color  depends  upon 
a  certain  amount  of  sunshine  and  exposure  to  light.  Plants  known 
to  be  capable  of  producing  the  color  will  show  it  to  only  a  small  degree 
if  conditions  for  anthocyanin  development  are  adverse,  while,  on  the 
other  hand,  races  in  which  it  does  not  normally  appear  conspicuously 
will  produce  it  under  conditions  of  sudden  exposure  to  direct  sun- 
shine or  sometimes  as  a  result  of  mutilation  caused  by  animals  or 
insects.  The  development  of  anthocyanin  is  a  matter  of  degree,  for 
the  potentiality  for  its  development  is  not  entirely  absent  from  any 
race  so  far  obtained.  In  the  viridis  race  we  have  it  in  its  lowest  and 
in  the  H6  race  in  its  highest  development.  Crosses  between  high  and 
low  anthocyanin  races  (other  than  19. e8  mentioned  above)  in  general 
produced  Fx  plants  showing  the  darker  anthocyanin  of  the  H6  race, 
but  in  F2  produced  a  series  of  forms  showing  a  gradation  in  pigment 
from  one  parent  to  the  other.  In  most  cases  the  parental  types  were 
also  duplicated.  One  such  cross,  H6  X  viridis  e33,  gave  an  F1  more 
nearly  like  the  H6,  but  in  F2  the  types  were  distributed  as  follows: 
9  of  H6,  3  of  viridis,  and  3  distinctly  between  these  two  parental  types. 
The  segregation  of  anthO'Cyanin  has  been  observed  in  other  cultures 
(e26=  3  to  1),  but  has  not,  in  general,  given  sufficiently  regular 
results  to  warrant  the  drawing  of  conclusions  regarding  its  genetic 
basis.  The  analysis  can  only  proceed  when  facilities  are  available  to 
control  more  accurately  the  environmental  factors  which  alter  its 
development. 

DWAEF  II   (dll) 
Plate  48,  figure  2 

This  variation  first  appeared  in  culture  21.99,  which  was  the 
second  selfed  generation  from  achenes  obtained  from  Lyons,  France. 
It  is  characterized  by  a  very  small  rosette  of  slender  semi-scalaris 
leaves  which  are  blotched  with  yellow  and  yellowish  red  coloration, 
giving  them  the  appearance  of  being  about  half -dead.  Due  to  their 
peculiar  appearance  the  first  plants  were  thought  to  be  suffering  from 
poor  environment,  although  adjacent  plants  were  healthy.  The  plants 
when  mature  are  very  small  (3-6  inches  in  height),  the  stems  very 
fine  and  spreading.  In  the  first  culture  the  dwarf  effect  appeared  to 
be  recessive  (5  dwarfs  in  16  plants)  and  bred  true  in  the  next  gene- 
ration. Culture  22.159  from  21.99P7S,  a  normal  plant,  contained  51 
plants,  3  of  which  were  dwarf  II  and  3  somewhat  dwarfish  but  not 
typical  for  dwarf  II.     This  is  approximately  a  15  to  1  ratio,  and 


1924]  Collins:  Inheritance  in  Crepis  capillaris    (L.)    Wallr.  265 

indicates  that  there  may  be  duplicate  genes  for  dwarf  II ;  sufficient 
data  are  not  at  hand  to  establish  the  hypothesis.  Culture  22.160 
(from  21.99Pir„  a  normal  plant)  gave  84  normal  plants. 

The  yellow  appearance  of  the  leaves  in  dwarf  II  seems  to  be  a 
dominant  character  from  its  appearance  in  22.407,  Fx  of  the  cross 
22.169P22  X  22.261P4,  the  male  parent  being  a  dwarf  II  plant  from 
a  pure  culture.  Inasmuch  as  the  Fx  plants  are  not  dwarfish,  it  appears 
that  the  yellowing  and  dwarfing  may  be  due  to  separate  but  probably 
linked  genes.  All  the  dwarf  II  plants  which  have  appeared  were 
yellowish,  and  we  may  therefore  assume  that,  instead  of  linkage, 
the  appearance  of  dwarf  II  is  dependent  on  the  presence  in  the  zygote 
of  the  dominant  gene  causing  yellowing. 

DWARF  III   (dill) 
Plate  49,  figure  1 

This  variation  first  appeared  in  1919  culture  e5.  It  reappeared  in 
1921  in  a  culture  (21.76)  which  came  from  the  same  source  as  e5. 
The  ratio  of  normal  to  dwarf  III  in  21.76  was  15  to  1,  and  in  the 
progeny  of  21.76?!  (culture  22.117)  3  to  1.  (See  table  10  for  data.) 
Dwarf  III  was  at  first  called  'semi-lethal, '  because  of  the  high  mortality 
in  this  class  of  plants.  These  plants  remain  very  much  smaller  than 
their  normal  sibs  during  the  rosette  stage  and  reach  maturity  much 
later.  A  large  percentage  die  after  they  have  formed  a  rosette  and 
before  they  reach  the  flowering  stage. 

This  variation  appeared  in  several  members  of  the  same  stock 
which  produced  revolute,  viridis,  and  pallid. 

SPREADING   (sp) 
Plate  49,  figure  2 

A  lax,  open-branching  habit  which  appeared  in  20.37,  the  French 
stock  of  Crepis.  The  stems  and  branches  are  long  and  slender,  appear- 
ing to  be  so  weak  they  cannot  support  themselves  in  upright  position. 
Dwarf  II  appeared  in  this  race  and  all  have  this  spreading  habit. 
Data  from  crosses  (21.26  and  22.173,  table  10)  show  that  it  is  a  reces- 
sive character.  When  the  same  plant  (20.37P3)  was  crossed  to  another 
erect  plant  (19.in.Pu),  it  behaved  as  a  dominant  (21.28,  22.41,  and 
22.43,  table  10).  Of  the  F2  cultures,  only  22.173  was  grown  under 
desirable  conditions;  the  others  were  overcrowded  in  greenhouse  and 
lath  house,  which  interfered  with  proper  development  of  this  char- 
acter. 


266 


University  of  California  Publications  in  Agricultural  Sciences       [Vol.  2 


PROCUMBENT   (p) 

This  variation  is  similar  in  appearance  to  spreading.  It  first 
appeared  in  culture  20.40,  which  came  from  achenes  sent  from  the 
Azores  Islands.  Unlike  spreading,  it  seems  to  be  dominant,  the  Fx 
plants,  21.28  (from  20.40P0  X  20.111PJ,  being  of  the  procumbent 
type.     The  F2  cultures  were  grown  under  crowded  and  unfavorable 

TABLE  10 
Segregation  of  Plant  Characters 


Segregation 

Culture  No. 

Normal 

Variant 

21.76 
Calculated  15:1 

57 
57.19 

4  dwarf  III 
3.81 

Deviation 

0.19  db  1.28 

22.159 
Calculated  15:1 

48 
47.81 

3  dwarf  II 
3.19 

Deviation 

0.19  ±  1.17 

22.117 
Calculated  3:1 

12 
12 

4  dwarf  III 
4 

Deviation 

0.0  ±  1.17 

22.99 
Calculated  3:1 

11 
12 

5  dwarf  II 
4 

Deviation 

1.0  ±  1.17 

22.173 
Calculated  3:1 

70  erect 
72  erect 

26  spreading 
24  spreading 

Deviation 

2.0  ±  2.86 

22.41 
22.43 

Total 
Calculated  1 :3 

18 
5 

23 
19.2 

39  spreading 
15  spreading 

54 

57.8 

Deviation 

3.8  ±  2.56 

1924]  Collins:  Inheritance  in  Crepis  capillaris   (L.)    Wallr.  267 

conditions  which  made  accurate  classification  difficult  and  uncertain. 
One  F2  gave  a  1  to  1  ratio  and  another  the  ratio  2  procumbent  to  1 
normal. 

ERECT   (e) 
Plate  50,  figure  1 

A  strain  characterized  by  erect  habit  of  growth,  large  stiff  lateral 
branches,  and  a  thick  rigid  central  axis.  The  branches  make  an  acute 
angle  with  the  axis,  the  whole  plant  having  the  form  of  an  inverted 
cone.  This  form  was  selected  from  the  F2  of  a  cross  between  the 
Danish  and  Swedish  stocks. 

PALE  A  (p) 
Plate  51,  figure  1 

The  nature  of  this  character  has  previously  been  discussed  (Collins, 
1921).  It  originally  appeared  in  an  Fx  hybrid  and  was  considered  a 
reversion  to  a  possible,  pre-composite,  ancestral  condition.  It  has 
appeared  in  every  case  in  hybrids,  never  in  inbred  races,  and  was 
probably  introduced  with  the  Danish  stock,  since  the  same  plant 
(17.198P2)  of  that  stock  is  in  the  pedigree  of  all  the  hybrids  which 
have  produced  palea.  Races  homozygous  for  palea  have  been 
obtained.  Preliminary  data  show  palea  to  be  conditioned  by  a  single 
recessive  gene. 

Linkage 

In  a  species  having  only  three  pairs  of  chromosomes,  it  would 
seem  fairly  easy  to  establish  groups  of  linked  genes,  especially  when 
the  species  was  known  to  be  more  or  less  polymorphic.  However,  it 
has  not  yet  been  possible  to  realize  this  end,  due  to  the  unexpected 
relations  of  some  of  the  genes  in  this  species.  For  instance,  there 
are  four  cases  of  complementary  recessive  genes,  and  three  characters 
dependent  upon  duplicate  dominant  genes.  The  determination  of 
linkage  groups  under  such  conditions  is  complicated  because  it  re- 
quires a  longer  time  to  obtain  races  with  a  known  and  tested  genotype. 

The  gene  for  bald  involucre  appears  from  data  in  tables  12  and  13 
not  to  be  linked  with  the  gene  for  smooth  ribs  nor  with  the  gene  for 
procumbent,  since  the  ratios  show  independent  segregation. 

It  is  of  course  obvious  that  linkage  must  occur  between  one  pair 
of  complementary  genes  for  smooth  ribs  and  one  pair  of  complemen- 
tary genes  for  revolute  leaves,  since  there  are  four  pairs  of  genes  and 


268 


University  of  California  Publications  in  Agricultural  Sciences       [Vol.  2 


only  three  pairs  of  chromosomes.  A  cross  involving  these  two  char- 
acters gave  the  following  results  (+  indicates  the  presence  and  —  the 
absence  of  the  character  named)  : 

TABLE  11 

Dihybrid  Segregation  of  Smooth  X  Revolute  in  a  Culture  which  Gave  a 
15:  1  Ratio  for  Each  Character  Separately 


Culture 
21.140 

Smooth  ribs 
Revolute  leaves 

: 

+ 

+ 

+ 
+ 

Total 

Observed 
Calculated 
57  :  3  :  3  :  1  : 

202 
224 

16 
11.79 

32 
11.79 

2 
3.93 

252 
252 

(o-c)2 
c 

1.98 

1.50 

34.64 

0.12 

X2  =  38.24 
P   =.0000 

The  calculated  numbers  agree  fairly  well  with  those  obtained 
except  in  the  third  class  where  the  observed  numbers  are  more  than 
twice  as  large  as  the  calculated  number.  This  class  may  have  been 
increased  at  the  expense  of  the  first  class  by  placing  in  it  some  plants 
which  genetically  belonged  in  the  latter.  The  observed  number  in 
the  first  class  is  considerably  less  than  the  calculated  number  for  that 
class.  These  figures  indicate  that  the  genes  are  arranged  in  the  three 
pairs  of  chromosomes  as  follows:  R,  s, —  (R'S')  (rV) — r,  S,  where 
primed  genes  are  the  complements  of  the  unprimed  genes.  Were  the 
linkages  as  follows  (R's)  and  (r'S),  the  F2  population  should  consist 
of  three  classes  in  the  proportion  of  14  :1 :1,  assuming  that  little  or 
no  crossing  over  occurs.  A  high  percentage  of  crossing  over  in  the 
latter  type  of  linkage  would  give  approximately  the  results  obtained. 
It  appears,  therefore,  that  either  the  dominants  are  linked,  as  stated 
above,  or  that  there  is  a  high  percentage  of  crossing  over  between  the 
linked  genes.  This  inference  can  be  tested  experimentally,  for  races 
have  been  obtained  which  gave  3  to  1  ratios  for  both  of  the  characters. 


Effects  of  Inbreeding 

The  flowers  of  Crepis  are  perfect  and,  although  self-fertilization 
can  take  place,  the  arrangement  of  the  stigmas  in  respect  to  the 
stamens  is  such  as  to  permit  cross-pollination  before  self-pollination 
can  be  naturally  effected.  The  stamens  are  united  into  a  tube  sur- 
rounding the  style,  and  the  pollen  is  shed  on  the  inside  of  this  tube. 


1924] 


Collins:  Inheritance  in  Crcpis  capillaris   (L.)    Wallr. 


269 


TABLE  12 

F2  Eesults  from  the  Dihybrid  Cross,  Glandular  and  Hairy  Midrib  X  Bald 
and  Smooth  Kibs,  Showing  Independent  Segregation 


Culture 
22.41* 

Observed 
segregation 

Calculated 
segregation 
9:3:3:1 

(o-c)2 
c 

Glandular 

and 

36 

41.01 

0.61 

Rib  Hairs 

Glandular 

and 

11 

13.68 

0.52 

Smooth 

Bald 

and 

20 

13.68 

2.84 

Rib  Hairs 

Bald 

and 

6 

4.56 

0.42 

Smooth 

73 

72.96 

X2  =  4.39 
P  =0.2264 

*Rib  hairs  vs.  smooth  in  this  culture  show  a  3  :  1  ratio. 


TABLE  13 

Showing  Independent  Segregation  in  F2  of  Dihybrid  Cross, 
Glandular-Erect  X  Bald-Procumbent 


Culture  No. 
22.41 

Observed 
segregation 

Calculated 
segregation 
9:3:3:1 

(o-c)2 
c 

Glandular — 
procumbent 

17 

20.25 

0.37 

Glandular — 
erect 

10 

6.75 

1.56 

Bald- 
procumbent 

7 

6.75 

0.01 

Bald- 
erect 

2 

2.25 

0.03 

36 

36.00 

X2  =  1.97 
P   =   .5773 

270  University  of  California  Publications  in  Agricultural  Sciences       [Vol.  2 

The  style  is  bifid  with  the  stigmatic  surface  on  the  adjacent  faces 
of  the  lobes.  With  the  beginning  of  anthesis  the  style  elongates, 
pushing  the  upper  end  out  from  the  stamen  tube  and  sweeping  the 
pollen  out  with  it  on  its  outer  surface.  The  stigmatic  lobes  then 
separate  and  assume  a  position  at  right  angles  to  the  style.  The  pollen 
at  this  stage  is  below  the  receptive  surface  of  the  stigma,  which  is, 
however,  exposed  to  insects,  the  means  by  which  cross-pollination  is 
effected.  Later  the  stigma  lobes  curl  into  a  short  spiral  which  brings 
the  receptive  surface  of  the  stigma  in  contact  with  its  own  pollen  or 
that  of  an  adjacent  floret  of  the  same  head.  Under  natural  conditions 
Crepis  is  often  cross-pollinated  by  insects,  and  this  preserves  a 
heterozygosity  of  the  germinal  material.  A  similarity  of  the  effects 
of  continued  inbreeding  in  Crepis  to  the  effects  of  inbreeding  in  maize 
has  been  noted  (Collins,  1920).  It  was  shown  that  inbreeding  caused 
a  reduction  in  the  size  of  the  plants  and  increased  the  length  of  the 
vegetative  period.  Other  data  are  now  available  which  show  in 
another  way  the  general  heterozygosity  of  Crepis  capillaris  as  it 
occurs  in  a  wild  state.  Thus  the  seed  collected  from  a  few  wild  plants 
near  Eureka,  California,  has  been  the  source  of  the  following  races: 
viridis,  scalaris-e28,  pallid,  and  revolute  (leaf  form  variations)  ;  of 
three  types  of  partial  albinos  (chlorophyll  development)  ;  and  of  the 
variations,  dwarf  III  and  fasciation  (the  plant  as  a  whole).  From 
the  Berkeley  wild  plants  we  have  obtained  plants  with  smooth  ribs 
and  the  leaf  form  H6 ;  from  England,  the  leaf  form  simplex-Z9 ;  from 
France,  dwarf  II,  spreading,  chlorina,  and  tubular  flowers.  Palea 
probably  came  from  the  Danish  material.  As  mentioned  in  another 
section,  bald  has  appeared  independently  in  the  cultures  from  six 
different  geographical  regions.  The  Eureka  stock  has  produced  the 
greater  number  of  new  races.  This  is  not  taken  to  mean  that  it  is 
necessarily  more  heterozygous  but  that  many  more  plants  from  this 
source  have  been  under  observation.  We  have  presented  here  an 
instance  of  a  remarkable  germinal  diversity  in  locally  developed 
strains  of  a  single  species.  Although  many  of  the  characters  appeared 
only  after  hybridization  between  local  races  or  stocks,  the  evidence 
does  not,  except  in  a  few  cases,  show  these  characters  to  be  due  to 
complementary  factors.  The  appearance  of  bald  from  such  widely 
separated  localities  as  Chile  and  Sweden  and  from  other  less  widely 
separated  localities  is  of  particular  interest,  for  it  shows  that  either  a 
certain  locus  of  the  germinal  material  mutates  more  readily  than 
others  or  that  all  these  local  races  have  originated  from  a  single  stock 


1924]  Collins:  Inheritance  in  Crepis  capillaris   (L.)    Wallr.  271 

in  which  this  gene  was  present ;  the  former  is,  however,  more  probable, 
for  it  has  been  shown  in  Drosophila  (Sturtevant,  1921)  that  certain 
loci  are  more  mutable  than  others.  Additional  evidence  that  this  is 
the  case  is  found  in  the  fact  that  a  similar  variation,  bald,  has  been 
found  to  occur  in  at  least  four  other  species,  C.  bursifolia,  C.  biennis, 
C.  aspera,  and  C.  dioscoridis.  A  similar  germinal  diversity  among 
local  races  of  Drosophila  m-elanog  aster  from  equally  widely  separated 
localities  has  not  been  found,  and  Sturtevant  suggests  that  this  may 
be  due  to  a  frequent  transportation  of  individuals  from  one  locality 
to  another.  The  chances  are  probably  as  great  for  transportation  of 
Crepis  seeds  along  with  agricultural  seeds  as  for  the  transportation 
of  Drosophila  among  fruits. 

It  is  possible  that  some  of  these  variations  might  have  arisen  from 
mutations  occurring  in  the  cultures  under  observation.  A  study  of 
the  wild  plants  in  the  fields  about  Eureka,  however,  disclosed  the 
fact  that  some  of  the  forms  obtained  in  the  greenhouse  by  inbreeding 
were  also  appearing  there  among  wild  plants.  In  this  material  it  is 
impossible  to  say  whether  any  new  recessive  variation  appeared  as  the 
result  of  a  recent  gene  mutation  or  the  segregation  of  a  recessive  from 
a  heterozygous  parent  stock. 

Variations  in  Chlorophyll 

A  number  of  different  variations  involving  a  loss  of  chlorophyll 
have  appeared.  These  variations  are  evident  in  the  seedling  stage, 
but,  unlike  the  usual  albinic  condition  in  seedling  plants,  most  of  these 
albino  types  develop  sufficient  chlorophyll  as  the  plant  grows  to  enable 
the  plant  to  live.  One  type  of  pure  white  seedling  always  dies  in  the 
seedling  stage.  The  other  types  are  either  pure  yellow  or  yellowish 
green.  The  percentage  of  seedling  mortality  in  these  classes  is  higher 
than  in  pure  green  seedlings. 

A  complete  analysis  of  the  genetic  relations  of  these  different  types 
has  not  yet  been  possible,  but  a  sufficient  study  has  been  made  to 
warrant  a  preliminary  report  in  this  general  account  of  variations  in 
Crepis  capillaris. 

CHLOEINA  (C) 

Chlorina  signifies  a  chlorophyll  deficiency  in  seedling  and  mature 
plants.  The  middle  portion  of  the  leaves  of  chlorina  plants  is  yellow- 
ish, but  both  tip  and  base  contain  more  or  less  chlorophyll  and  thus 
it  is  possible  for  the  plant  to  function.    This  character  first  appeared 


272 


University  of  California  Publications  in  Agricultural  Sciences       [Vol.  2 


in  culture  21.99.  In  1922  a  culture  of  six  chlorina  plants  was  obtained. 
When  these  chlorina  plants  were  crossed  with  normal  green  plants, 
the  two  classes  of  plants — normal  and  chlorina — appeared  in  the 
progeny  in  equal  numbers,  thus  indicating  that  the  chlorina  plants 
were  heterozygous  for  green.  Self-fertilization  of  the  green  resulted 
in  only  green  progeny.  The  seedling  progeny  from  self-fertilized 
chlorina  plants  consisted  of  three  classes :  pure  yellow,  pale  green,  and 
normal  green,  in  the  ratio  1  to  2  to  1.  The  yellow  seedlings  died,  the 
pale  green  ones  developed  into  chlorina  plants,  and  the  green  seed- 
lings produced  only  green  plants.  The  gene  for  chlorina  is  therefore 
dominant  and  has  a  lethal  action  when  homozygous. 

TABLE  14 

Segregation  of  Seedling  Progeny  of  Self-fertilized  Chlorina  Plants 


Culture  No. 

Green 

Pale  green 

Yellow 

24.171 
24.173 
24 . 174 

46 
13 
66 

60 

17 

? 

26 

6 

33 

Total 

125 

77 

65 

Observed 
Calculated  3:1 

202 
200.25 

65 
66.75 

Deviation 

1.25  ±4. 77 

In  table  14  the  seedlings  in  culture  24.174  intergraded  in  such  a 
way  that  it  was  impossible  to  make  an  accurate  segregation  of  pale 
green  from  green;  consequently  the  two  classes  are  combined  in  the 
table.  Separation  of  the  two  green  types  in  other  cultures  was  less 
difficult,  although  it  is  apparent  that  some  pale  green  plants  have  been 
included  in  the  green  class. 


GOLDEN  YELLOW  (y) 

The  type  known  as  golden  yellow  behaves  as  a  monohybrid  reces- 
sive as  shown  by  data  in  table  15. 

These  golden  yellow  seedlings  gradually  develop  chlorophyll  and 
finally  reach  maturity,  although  growing  much  more  slowly  than 
their  green  sibs.  These  plants  can,  however,  be  distinguished  in  the 
mature  stage,  due  both  to  size  and  to  the  peculiar  distribution  of  the 
chlorophyll.     They  produce  mature  rosettes  that   show  a  mottling 


1924 


Collins:  Inheritance  in  Crepis  capillaris   (L.)    Wallr. 


273 


of  yellow  and  green  through  the  leaves,  which  looks  much  like  the 

plant  disease  known  as  '  mosaic, '  or  rosettes  on  which  the  central  and 

thus  younger  leaves  of  the  plant  are  a  clear  yellow.     These  yellow 

leaves  later  develop  chlorophyll  and  become  normally  green. 

It  would  appear  from  table  15  that  the  golden  yellows  would  be 

homozygous  recessives ;  but  this  is  not  the  case,  for  the  seedlings  from 

selfed  'yellow  center'  and  from  'mottled'  plants  show  some  of  them 

to  be  heterozygotes.     Only  one  plant  has  yet  been  found  which  was 

homozygous  for  yellow. 

TABLE  15 

monohybrid  segregation  of  golden  yellow  in  the  progeny  of 
Green  Plants 


Culture  No. 

Progeny  segregation  of  seedlings 

1921 

Green 

Yellow 

177P13 

10 

3 

177P16 

12 

3 

177P17 

278 

84 

177P38 

13 

5 

177P40 

15 

3 

177P78 

36 

10 

177P124 

23 

6 

Total 

387 

114 

Calculated  3:1 

375.75 

125.25 

Deviation 

11.25  ±  6.54 

That  there  are  other  genes  which  also  produce  yellow  seedlings  is 
evident  from  table  16.  The  three  plants  P39,  66,  and  76  were  green 
as  seedlings  and  normal  green  in  the  mature  stage.  They  apparently 
were  heterozygous  for  two  recessive  genes  which  produced  the  same 
or  a  very  similar  type  of  yellow.  The  progeny  of  P25  indicate  still 
another  type  of  yellow  indistinguishable  phenotypically  from  those 
already  mentioned.  Here  the  production  of  chlorophyll  in  the  seed- 
ling stage  is  dependent  on  the  simultaneous  presence  of  two  dominant 
genes,  and  the  absence  of  either  one  results  in  a  yellow  type  of 
seedling. 

Trow  (1916)  reports  a  similar  case  of  complementary  recessive 
genes  in  the  production  of  albino  seedlings  in  Senecio,  another  genus 
of  the  Compositae. 


274 


University  of  California  Publications  in  Agricultural  Sciences       [Vol.  2 


TABLE  16 

Showing  Seedling  Segregation  in  the  Progeny  of  Green  Plants  Indicating 

Complementary  Eecessive  Genes  for  Golden  Yellow  and 

Duplicate  Genes  for  Chlorophyll 


Progeny  segregation  of  seedlings 

Culture  No. 

Green 

Yellow 

21.177P39 
21.177P66 
22.177P76 

44 
13 
45 

3 
1 
3 

Total 

102 

7 

Calculated  15:1 

102.19 

6.81 

Deviation 

0.19  ±  1.70 

21.177P25 

Calculated  9:7 

22 
19.687 

13 
15.312 

Deviation 

2.312  ±  1.98 

VIEESCENT  YELLOW  (v) 

A  third  type  of  seedling  called  virescent  yellow  has  a  small  amount 
of  green  color  in  addition  to  the  yellow.  These  seedlings,  like  the 
yellow  ones,  may  produce  two  types  of  mature  plants,  namely,  pure 
green  plants  and  green  plants  with  pale  green  younger  leaves  at  the 
center  of  the  rosette.  The  data  at  present  indicate  that  virescent 
plants  are  produced  when  a  gene  dominant  to  yellow  but  recessive  to 
green  is  present  with  the  gene  for  yellow,  which  changes  yellow  seed- 
lings to  virescent  and  yellow-center  rosettes  to  pale  green  centers. 
When  virescent  plants  are  self ed,  then  green,  virescent,  and  yellow  are 
obtained,  but  no  virescent  plants  have  appeared  in  the  progeny  of 
yellow  plants. 

It  is  hoped  that  in  another  place  it  will  be  possible  to  publish 
more  extensive  data  and  a  complete  discussion  of  the  inheritance  of 
chlorophyll  deficient  characters  in  Crepis  which  cannot  be  given  at 
this  time. 


1924]  Collins:  Inheritance  in  Crepis  capillaris   (L.)    Wallr.  275 


GENERAL   DISCUSSION 

In  order  to  establish  and  preserve  true  breeding  strains  of  the 
different  types  observed  in  the  eultures,  type  plants  were  self- 
pollinated  in  successive  generations.  This  most  intense  type  of 
inbreeding  affected  these  cultures  in  very  much  the  same  way  as 
inbreeding  has  affected  maize.  Reduction  in  size  and  a  slower  rate 
of  growth  were  the  most  noticeable  results  of  inbreeding  together 
with  a  slight  increase  in  sterility.  Most  of  the  experiments  to  show 
the  effect  of  inbreeding  in  plants  have  been  with  domesticated  forms 
in  which  it  is  possible  to  have  a  genotypic  constitution  that  might  not 
exist  in  a  wild  state,  because  characteristics  which  would  unfit  the 
individual  for  survival  in  natural  conditions  are  often  preserved 
under  the  artificial  conditions  of  cultivation.  The  inference  is  that 
wild  species  would  differ  in  fewer  genes  than  their  cultivated  relatives. 
However,  the  inbreeding  experiments  on  Drosophila  (Castle,  1906) 
produced  no  bad  effects.  Collins  (1919)  states  that  self-fertilization 
in  teosinte,  a  wild  relative  of  maize,  causes  no  loss  of  vigor  such 
as  is  known  to  occur  in  maize.  On  the  other  hand,  Darwin  (1876) 
concluded  that  wild  species  which  are  naturally  cross-pollinated  are, 
on  the  whole,  adversely  affected  by  inbreeding.  It  appears  then  that 
the  results  of  inbreeding  any  race,  cultivated  or  wild,  would  be  an 
index  to  its  genotypic  heterozygosity  or  homozygosity.  With  this  as 
a  criterion,  there  is  indicated  a  condition  of  germinal  heterozygosity 
in  Crepis  capillaris.  There  appears  to  be  a  certain  similarity  between 
wild  heterozygous  species  of  Crepis  and  the  cultivated  races  of  maize 
in  the  type  of  recessive  genes  which  persist  in  the  genotype.  In  maize, 
a  number  of  genes  are  present  which  produce  characters  that  are  so 
abnormal  (sterility,  extreme  dwarfs,  albinos)  that  they  are  propa- 
gated only  with  difficulty  and  would  seldom  be  found  under  natural 
conditions.  Examples  of  similar  forms  have  appeared  in  inbred 
strains  of  Crepis.  It  may  therefore  be  considered  that  natural  selec- 
tion has  not  eliminated  these  genes  from  the  germinal  material  of  the 
wild  species.  The  genes  in  Crepis  which  affect  vigor  also  produce 
results  comparable  to  similarly  acting  genes  in  maize. 

Evidence  of  the  genotypic  heterozygosity  of  capillaris  has  also 
been  gained  from  another  source.  Seeds  have  been  obtained  from 
widely  separated  localities  and  grown  side  hy  side  in  the  greenhouse 


276  University  of  California  Publications  in  Agricultural  Sciences       [Vol.  2 

and  garden.  The  number  of  different  forms  resulting  either  in  the 
first  or  later  generations  and  as  a  result  of  controlled  cross-pollinations 
show  that  the  germinal  material  was  indeed  far  from  homozygous. 
It  is  of  importance,  because  of  some  current  theories  regarding  the 
influence  of  the  habitat  upon  the  genotype  of  a  local  species  (Tures- 
son,  1922),  to  observe  the  behavior  of  these  various  forms  when  grown 
in  as  nearly  identical  conditions  as  can  ordinarily  be  furnished  in  a 
greenhouse  or  garden.  Plants  belonging  to  many  different  genera 
were  collected  by  Turesson  from  contrasted  habitat  localities  in 
Sweden  and  grown  together  in  a  common  garden.  He  found  that 
in  general  each  particular  type  of  a  species  found  in  each  of  several 
different  habitats  maintained  its  characteristics  in  the  absence  of  the 
habitat  to  which  it  seemed  especially  modified.  He  sees  in  such 
phenomena  a  refutation  of  the  theory,  now  generally  held,  that  the 
form  predominating  in  a  given  locality  occurred  as  a  chance  mutation 
or  recombination  and  was  preserved  through  natural  selection.  The 
theory  substituted  for  this  is  Lamarckianism  expressed  in  modern 
terminology,  namely,  habitat  causes  a  change  in  the  fundamental 
genotype  of  the  species  such  that  a  phenotype  is  developed  which 
permits  the  plant  to  nourish  in  a  specialized  habitat.  His  report 
deals  principally  with  three  types  of  plants  in  all  his  species,  viz., 
dwarf  forms,  upright  or  erect  forms,  and  spreading  or  procumbent 
forms,  each  of  which  was  found  in  a  location  favorable  to  the  existence 
of  that  type  while  unfavorable  to  the  other  types;  and  each  thus 
becomes  a  demonstration  of  the  effects  of  natural  selection.  In  our 
study  of  Crepis  forms  we  have  not  been  fortunate  enough  to  study 
wild  populations  of  Crepis  in  all  of  the  localities  from  which  we  have 
obtained  seed,  but  we  have  produced  hereditary  strains  of  erect  forms, 
spreading  forms,  and  dwarf  forms  from  the  same  habitat  at  Eureka, 
a  fact  which  does  not  especially  favor  the  existence  of  any  one  type. 
Dwarf  forms  have  also  appeared  in  cultures  from  other  places  (France 
and  Denmark),  whose  definite  habitat  characteristics  are  unknown 
to  us.  Similar  plant  forms  are  well  known  to  occur  sporadically  in 
many  wild  and  domesticated  species.  Mutations  giving  rise  to  pros- 
trate and  dwarf  types  in  plants  are  not  infrequent  when  compared 
to  other  types  of  change.  If  we  accept  the  idea  of  a  genoiypic  response 
of  the  species  to  the  habitat,  are  we  not  also  admitting  the  inconstancy 
of  the  gene,  a  theory  which  is  no  longer  tenable?  Continuing  the 
assumption,  it  is  not  clear  why  these  different  hereditary  types,  such 
as  we  have  in  Crepis,  remain  constant  in  a  single  unvarying  habitat. 


1924]  Collins:  Inheritance  in  Crepis  capillaris   (L.)    Wallr.  277 

The  very  fact  that  they  do  not  approach  a  common  type  under  culti- 
vated conditions  supports  the  theory  of  the  constancy  of  the  gene  and 
is  evidence  of  the  inability  of  the  habitat  to  induce  genotypic  changes. 
The  occurrence  of  duplicate  genes  in  other  plants  has  brought 
forth  the  opinion  that  they  may  indicate  the  presence  of  duplicated 
chromosomes.  Three  cases  of  duplicate  genes  have  been  found  in 
Bursa  (Shull,  1920),  a  plant  having  32  chromosomes  (4  X  8),  while 
a  case  of  triplicate  genes  is  reported  in  a  wheat  (Nilsson-Ehle,  1909) 
which  has  42  chromosomes.  This  number  is  three  times  the  number 
(14)  found  in  several  species  of  Triticum  (Sax,  1921).  Several  pairs 
of  duplicate  genes  have  been  found  in  Crepis  capillaris.  No  plants 
producing  such  ratios  have  been  examined  cytologically,  but  in  no 
visible  way  do  they  differ  from  plants  which  give  3  to  1  ratios  for 
the  same  characters.  From  what  is  known  regarding  the  effect  of 
duplication  of  single  chromosomes  or  of  whole  sets  of  chromosomes 
in  Datura  (Blakeslee,  1922)  and  in  Nicotiana  (Clausen  and  Good- 
speed,  1924),  it  is  difficult  to  suppose  duplication  of  chromosomes  has 
occurred  here.  That  we  have  parallel  mutations  in  identical  loci 
of  two  chromosomes  of  the  same  kind  derived  from  a  form  with  a 
different  number  by  some  meiotic  irregularity  is  equally  improbable, 
for  capillaris  has  but  three  pairs  of  chromosomes,  no  two  similar 
enough  in  size  to  be  construed  as  duplicates.  There  are  several 
other  ways  to  account  for-  the  appearance  of  duplicate  genes,  some 
of  which  have  been  discussed  by  Shull  (1918).  Four  of  these  possi- 
bilities are  (a)  the  occurrence  of  similar  gene  mutations  in  different 
chromosome  pairs;  (6)  the  mating  of  non-homologous  chromosomes; 
(c)  duplication  of  entire  chromosomes;  and  (d)  duplication  of 
sections  of  chromosomes.  The  possibility  of  a  chromosomal  dupli- 
cation as  the  cause  of  the  origin  of  duplicate  genes  in  Crepis  is  very 
unlikely,  as  has  been  shown  above.  The  other  possibilities  cannot  be 
dealt  with  so  readily.  It  would  appear,  however,  that,  had  duplica- 
tion of  a  section  of  a  chromosome  taken  place,  other  characters,  the 
genes  for  which  were  located  in  the  duplicated  section,  should  show 
similar  inheritance  ratios.  As  a  matter  of  fact,  two  other  characters 
in  Crepis  capillaris  give  ratios  of  15  to  1,  but  in  the  one  case  tested 
(revolute  X  smooth  ribs)  the  type  of  linkage  demanded  by  such  an 
hypothesis  was  not  obtained.  Mating  of  non-homologous  chromosomes 
should  also  result  in  duplication  of  other  genes  which  should  show 
linkage  relations.  Although  only  a  small  amount  of  critical  data  is 
as  yet  available,  no  confirmation  of  the  linkage  relations  demanded 


278  University  of  California  Publications  in  Agricultural  Sciences       [Vol.  2 

by  these  two  methods  of  gene  duplication  has  been  obtained.  Shull 
rejected  the  idea  of  the  occurrence  of  two  independent  mutations  as 
a  cause  of  duplication  of  genes  in  Bursa  on  the  ground  that  the  char- 
acters were  of  such  a  complex  nature  that  the  occurrence  of  two 
independent  mutations  producing  identically  the  same  somatic  results 
was  on  the  verge  of  impossibility.  The  characters  in  Crepis  for  which 
there  are  duplicate  genes  cannot  be  considered  as  complex,  and  the 
occurrence  of  similar  mutations  in  non-homologous  chromosomes 
therefore  seems  at  the  present  time  to  be  the  more  reasonable  explana- 
tion of  the  origin  of  duplicate  genes  in  this  species. 

Sturtevant  (1921)  has  shown  that  some  points  in  the  germinal 
material  of  a  given  species  are  more  susceptible  to  mutations  than 
others.  There  is  evidence  that  such  a  mutating  locus  occurs  in 
capillaris,  for  the  same  character,  bald,  has  appeared  in  a  number  of 
strains  derived  from  widely  separated  localities.  The  identity  of 
these  genes  for  bald  has  been  proved  in  all  cases  except  one  (France) 
by  crosses  in  which  they  proved  to  be  allelomorphic.  That  a  certain 
locus  may  mutate  in  the  same  way  in  other  species  is  at  least  indicated 
by  the  fact  that  this  character  is  now  known  to  occur  in  four  other 
species,  none  of  which  has  been  grown  extensively  among  our  cultures. 
The  gene  for  bald  is  recessive  in  capillaris  and  is  also  recessive  in  the 
species  cross,  setosa  X  capillaris. 

No  less  interesting  and  unique  is  the  group  of  complementary 
genes  found  in  C.  capillaris  where  the  appearance  of  three  such  pairs 
of  genes  are  concerned  with  the  inheritance  of  leaf  characters  and  a 
fourth  with  chlorophyll.  It  is  not  strange,  however,  that  a  greater 
number  of  complex  gene  relations  should  be  encountered  in  a  species 
containing  a  low  number  of  chromosome  pairs  than  in  species  having 
a  larger  number,  unless  the  larger  number  results  from  reduplication. 
There  is  probably  a  minimum  number  of  genes  which  is  necessary 
in  any  species,  and  there  is  no  reason  to  believe,  a  priori,  that  a  species 
with  a  larger  number  of  chromosomes  need  have  a  correspondingly 
larger  number  of  genes.  There  is  also  evidence  from  Drosophila  that 
the  genes  are  distributed  at  random  in  each  chromosome  (except  in 
cases  of  multiple  allelomorphs)  and  among  the  chromosomes.  When 
this  basic  number  of  genes  is  distributed  among  a  large  number  of 
chromosomes,  more  characters  will  show  simple  types  of  inheritance. 
When  this  basic  number  is  distributed  in  a  fewer  number  of  chromo- 
somes, there  will  necessarily  result  more  complex  types  of  inheritance. 


1924]  Collins:   Inheritance  in   Crepis  capillaris    (L.)    Wallr. 


SUMMARY 

1.  Plants  of  Crepis  capillaris  are  largely  cross-fertilized,  and  this 
mode  of  reproduction  operates  to  maintain  a  condition  of  genotypic 
heterozygosity. 

2.  Inbreeding  wild  plants  thus  produced  results  in  the  production 
of  a  number  of  pure  races  which  show  loss  of  vigor  and  reduction 
in  size  similar  to  the  effects  produced  by  inbreeding  maize. 

3.  Four  sets  of  duplicate  genes  are  found  to  be  responsible  for 
the  inheritance  of  four  different  characters.  Two  of  these  characters 
are  shown  not  to  be  linked.  Duplicated  genes  do  not  indicate  dupli- 
cated chromosomes,  for  each  pair  is  morphologically  different  from 
the  others. 

4.  The  recessive  character  'bald'  has  appeared  in  a  number  of 
unrelated  strains.  This  is  evidence  that  a  certain  locus  in  one 
chromosome  pair  mutates  more  frequently  in  the  same  way  than  do 
other  loci.  The  appearance  of  bald  in  other  species  may  be  due  to 
a  similar  gene  in  each  of  these  four  species. 

5.  Several  types  of  chlorophyll  variations  have  appeared.  Some 
show  monohybrid  recessive  relations  when  contrasted  with  the  normal 
condition,  while  others  show  more  complex  relations. 

6.  The  different  forms  from  widely  separated  localities  show  no 
tendency  to  approach  a  common  type  when  grown  continuously  in 
the  same  place. 


It  is  with  pleasure  that  the  author  acknowledges  the  helpful  advice 
given  by  Professor  Babcock  and  Professor  Clausen  throughout  the 
progress  of  the  work. 


280  University  of  California  Publications  in  Agricultural  Sciences       [Vol.  2 


LITERATURE  CITED 

Babccck,  E.  B.,  and  Collins,  J.  L. 

1920.     Interspecific  hybrids  in  Crepis.     I.     Crepis  capillaris  (L.)   Wallr.  X  C. 
,     tectorum  L.    Univ.  Calif.  Publ.  Agr.  Sci.,  vol.  2,  pp.  191-204. 

Blakeslee,  A.  F. 

1922.  Variations  in  Datura  due  to  changes  in  chromosome  number.  Am.  Nat., 
vol.  61,  pp.  16-31. 

Castle,  W.  E.,  Carpenter,  F.  W.,  et  al. 

1906.  The  effects  of  inbreeding,  cross-breeding,  and  selection  upon  the  fer- 
tility and  variability  of  Drosophila.  Proc.  Am.  Acad.  Arts  and  Sci., 
vol.  41,  pp.  731-786. 

Clausen,  E.  E.,  and  Goodspeed,  T.  H. 

1924.  Inheritance  in  Nicotiana  tahacum.  IV.  The  trisomic  character  ' '  en- 
larged. "     Genetics,  vol.  9,  pp.  181-197. 

Collins,  G.  N. 

1919.  Intolerance  in  maize  to  self-fertilization.     Jour.  Wash.  Acad.  Sci.,  vol. 

9,  pp.  309-312. 

Collins,  J.  L. 

1920.  Inbreeding  and  cross-breeding  in  Crepis  capillaris    (L.)   Wallr.     Univ. 

Calif.  Publ.  Agr.  Sci.,  vol.  2,  pp.  205-216. 

1921.  Eeversion  in  composites.     Jour.  Hered.,  vol.   12;  pp.   129-133. 

1922.  Culture    of   Crepis   for   genetic   investigations.      Jour.    Hered.,    vol.    13, 

pp.   329-355. 

CORRENS,   C. 

1912.     Die  neuen  Vererbungsgesetze  (Berlin),  75  pp. 

Darwin,  C. 

1876.     The   effects   of   cross-   and  self-fertilization   in   the   vegetable   kingdom 
(London),  482  pp. 
Harris,  J.  A. 

1912.  A  simple  test  of  the  goodness  of  fit  of  Mendelian  ratios.  Am.  Nat., 
vol.  46,  pp.  741-745. 

Kristofferson,  Karl  B. 

1923.  Monohybrid  segregation  in  Malva  species.     Hereditas,  vol.  4,  pp.  44-54. 

Nilsson-Ehle,  H. 

1909.  Kreuzungsuntersuchungen  an  Hafer  und  Weizen.  Lund's  Univ.  Ars- 
skrift,  vol.  5,  pp.  1-122. 

Basmuson,  Hans. 

1916.  Kreuzungsuntersuchungen  bei  Beben.  Zeitschr.  f.  Indukt.  Abstamm. 
Vererb.,  vol.   17,  pp.  1-52. 

Rau,  Venkata 

1923.     Inheritance  of  some  morphological  characters  in  Crepis  capillaris   (L.) 
Wallr.     Univ.  Calif.  Publ.  Agr.  Sci.,  vol.  2,  pp.  217-242. 
Sax,  Karl 

1921.     Chromosome  relationships  in  wheat.     Science,  n.s.,  vol.  54,  pp.  413-415. 


1924]  Collins:  Inheritance  in  Crepis  capillaris   (L.)    Wallr.  281 

Sears,  Paul  B. 

1922.  Variation  in  cytology  and  gross  morphology  of  Taraxacum.     Bot.  Gaz., 

vol.   73,  pp.  425-446. 

Shoemaker,  D.  N. 

1919.  A  study  of  leaf  characters  in  cotton  hybrids.     Am.  Breed.  Assoc,  vol.  5, 

pp.   110-110. 
Shull,  G.  II. 

1914.     Tiber  die  Vererbung  der  Blattfarbe   bei  Melandrium.     Ber.   Dent.   Bot. 

Gesellschaft,  vol.  31,  pp.  41-80. 
1918.     Duplication  of  leaf  lobe  factor  in  Bursa.     Brooklyn  Bot.  Garden,  Mem., 
vol.    1,  pp.  427-443. 

1920.  A  third  duplication  of  genetic  factors  in  shepherds  purse.     Science,  n.s., 

vol.  51,  pp.  590. 

1921.  Three  new  mutations  in  Oenothera  LamarcMana.     Jour.  Hered.,  vol.   12, 

pp.  354-363. 

Stork,  Harvey  E. 

1920.  Studies  in  the  genus  Taraxacum.     Torr.  Bot.  Club  Bull.  47,  pp.  199-210. 

Sturtevant,  A.  H. 

1921.  Genetic  studies  on  Drosopliiln  simulans  III.     Genetics,  vol.  6,  pp.   179- 

207. 
Tedin,  Olcf 

1923.  The  inheritance   of  pinnatifid   leaves   in   Camelina.      Hereditas,   vol.   4, 

pp.  59-64. 
Trow,  A.  H. 

1916.     On  "albinism"  in  Senecio  vulgaris  L.     Jour.  Gen.,  vol.  6,  pp.  65-74. 

TURESSON,   GOTE 

1922.  The  genotypical  response  of  the  plant  species  to  the  habitat.     Hereditas, 

vol.  3,  pp.  211-350. 


EXPLANATION  OF  PLATES 

PLATE  45 

Fig.  1.  A  rosette  of  the  viridis  race  on  the  left  with  a  pallid  rosette  on  the 
right. 

Fig.  2.  A  typical  rosette  of  the  scalaris  H6  race,  showing  blunt  lobes,  raffled 
Aving  on  midrib,  constricted  base  of  lateral  lobes,  and  a  twisting  of  the  lateral 
lobes. 


[282] 


UNIV.    CALIF.    PUBL.    AGRI.    SCI.    VOL.    2 


COLLINSI    PLATE   45 


Fig.  1 


Fig.  2 


PLATE  46 

Fig.  1.     A  rosette  of  simplex  Z9  on  the  left,  and  at  the  right  the  aberrant 
pinnatifid  type  which  appears  in  all  cultures. 

Fig.  2.     A  rosette  of  the  scalaris  e29  race. 


[284] 


UNIV.    CALIF.    PUBL.    AGRI.    SCI.    VOL.    2 


[COLLINS]    PLATE   46 


Fie.  1 


Fie.  2 


PLATE  47 

Fig.   1.     A  typical  rosette  of  the  pinnatifid  leaf,  scalaris  e28. 
Fig.  2.     A  rosette  showing  revolute  leaves. 


[286] 


UNIV.    CALIF.    PUBL.    AGRI.    SCI.    VOL.    2 


[COLLINSI    PLATE   47 


Fig.  1 


Fig. 


PLATE  48 

Fig.   1.     The  bicephalic  type  of  faseiation. 
Fig.  2.     A  mature  dwarf  II  plant. 


[288] 


UNIV.    CALIF.    PUBL.    AGRI.    SCI.    VOL.    2 


ICOLLINS]    PLATE   48 


% 


Fig.  1 


V 


IT 


Fig.  2 


PLATE  49 

Fig.   1.     Two  dwarf  III  plants  with  two  normal  sibs. 

Fig.  2.     A  typical  plant  from  the  race  with  the  spreading  habit. 


[290] 


UNIV.    CALIF.    PUBL.    AGRI.    SCI.    VOL.    2 


ICOLLINSI    PLATE   49 


KB 

w 


Vr.i>. 


feS* 


ft&ft 


/%wfc* 


Fig.  1 


fc     *A-A'\ 


Fig. 


PLATE  50 
Fig.   1.     A  typical  plant  of  the  erect  growth  habit. 


[292] 


UNIV.    CALIF.    PUBL.    AGRI.    SCI.    VOL.    2 


(COLLINSI    PLATE   50 


PLATE  51 

Fig.  1.     Palea  on  the  left  with  a  receptacle  of  a  normal  plant  on  the  right. 
Fig.  2.     Three  F,  rosettes  from  the  cross,  scalaris  X  simplex. 


[294J 


UNiV.    CALIF.    PUBL.    AGRI.    SCI.    VOl  .    2 


[COLLINSI    PLATE   51 


Fig.  1 


I 


Fig. 


PLATE  52 

Fig.  1.  Typical  leaves  from  two  plants  of  each  of  the  parent  strains  and  of 
the  F1}  together  with  one  leaf  from  each  of  eight  F2  plants,  which  show  the  results 
obtained  when  scalaris  and  simplex  plants  are  crossed.  Note  the  appearance  in 
F2  of  the  curved  terminal  lobe  typical  of  the  scalaris  grandparent. 


[296] 


UNIV.    CALIF,    PUBL.    AGRI.    SCI.    VOL.    2  (COLLINS,    PLATE   52 


